In collaborative research efforts across three institutions, neuroscientists, including 2012 NARSAD Young Investigator Grantee, Xiangmin Xu, Ph.D., of the University of California (UC) Irvine, used newly developed genetic and imaging technologies to study the activity of inhibitory neurons in the brain. The brain is made up of two types of cells—inhibitory and excitatory neurons. About 80 percent of neurons are excitatory and until now, using traditional scientific tools, researchers have only been able to study the excitatory neurons. It is widely believed that inhibitory neurons play a critical role in heightening plasticity in the young, but it was not known how.

The researchers, from UC Irvine, UC Los Angeles and Carnegie Mellon University in Pittsburgh, discovered that during heightened periods of learning in early development, contrary to prevailing scientific thought, inhibitory neurons actually reduce their activities. The reduction in activity weakens inhibition of the brain circuit and allows the neural connections to be remodeled (what is referred to as brain “plasticity”). The prevailing theory about inhibitory neurons had been that, as they mature, they reach an increased level of activity to foster optimal learning but that as the brain ages into adulthood and the inhibitory neurons continue to mature, they become even stronger to the point where they impede learning. This new work, published online in the journal Nature on August 25th, essentially disproves this hypothesis.
 
"When you're young you haven't experienced much, so your brain needs to be a sponge that soaks up all types of information. It seems that the brain turns off the inhibitory cells in order to allow this to happen," explains Sandra J. Kuhlman, Ph.D., Assistant Professor of Biological Sciences at Carnegie Mellon and a 2006 NARSAD Young Investigator Grantee. "As adults we've already learned a great number of things, so our brains don't necessarily need to soak up every piece of information. This doesn't mean that adults can't learn, it just means when they learn, their neurons need to behave differently."

The inhibitory neurons studied mediate an important part of early vision development and this new finding offers a new approach to correcting central visual disorders in children who suffer from early cataracts or “lazy eye” (amblyopia). The condition, often a result of improper brain development due to visual deprivation during childhood, can be permanent, even after surgery to remove cataracts or correct lazy eye. In contrast, when cataracts in adults are surgically corrected, normal vision is usually restored.

“The specific type of neurons that mediate the critical-period window during childhood development have not been well understood until now,” Dr. Xu said. “Our breakthrough outlines a new path for treatments that can restore normal vision in children who have had early vision disorders.”

Read the press release from UC Irvine

Read the press release from Carnegie Mellon University